populate issue introduced with 5.7.x

[SantoJambit]

Describe the bug
Using populate does not work as expected after an update. The last working version I found is 5.6.16. Did not try V6 yet, as it's not final.

I have the following tables:

class UserSkill {
    @PrimaryKey()
    id: number;
    
    @ManyToOne(() => User, { nullable: false })
    user: User;
    
    @ManyToOne(() => Skill, { nullable: false })
    skill: Skill;
...
}

class User {
    @PrimaryKey()
    id: string;

    @OneToMany({ entity: () => UserSkill, mappedBy: "user" })
    userSkills = new Collection<UserSkill>(this);
...
}

class Skill {
    @PrimaryKey()
    id: number;

    @Property({ nullable: false })
    label: string;

    @OneToMany(() => UserSkill, "skill")
    userSkills = new Collection<UserSkill>(this);
...
}

I left out parts that did not seem relevant.

I want to get all users that have a specified skill and list/populate all the skills each user has.
My Query was like this:

        const userSkills = await em.find(
            UserSkill,
            {
                skill: skills,
                user: {
                    accountEnabled: true,
                },
            },
            {
                populate: ["user.userSkills.skill", "user.userSkills.user"],
            }
        );

This was populating all of the user.userSkills.skill.* fields before 5.7.x, but afterwards I noticed user.userSkills.skill.label was not set. Interestingly, when I change the populate line to this, it works:

                populate: ["user.userSkills.skill", "user.userSkills.user", "skill"],

Just using "skill" doesn't work either:

                populate: ["user.userSkills.user", "skill"],

I don't care about "skill", as I already know the input skill. I care about all the other skills, which are available via user.userSkills.skill.

To Reproduce
Steps to reproduce the behavior:

1. Reproduce the above scenario
2. Try with 5.6.16 and then with v >= 5.7.x. Not sure which x is correct here, as versions 5.7.0 up to (and including) 5.7.11 give me a different error (TypeError: core_1.Utils.mergeConfig is not a function)

Expected behavior
Populate should work as before.

Additional context
I found an issue, which might be related, but was marked as fixed: #4339
I think it might have the same root cause, as "skill" exists in multiple places here too.

Versions

Dependency	Version
node	18.13.0
typescript	4.9.4
mikro-orm	5.7.x - 5.9.1
your-driver	postgresql

[B4nan]

I need to see a complete reproduction for such issues, including the data, you mentioned #4339, that issue is closed with a passing test case, so ideally adjust that test so it fails.

5.7.11 give me a different error (TypeError: core_1.Utils.mergeConfig is not a function)

This means you have a version mismatch, some of your packages are newer than the core package. But let's not deal with it (it's actually already fixed in recent versions which pin the internal dependencies), let's talk about the latest stable (which is 5.9.2, not 5.9.1, but I don't think there were relevant fixes in the last release anyway), or even better about the latest 5.x dev release.

---

FYI nullable: false is the default.

edit: I guess you are using joined strategy? also are we talking about how entities are hydrated or how they look when serialized?

[SantoJambit]

I have used the default loadStrategy so far. I wasn't aware of that option. I guess with postgres it makes sense to make joined the default loadStrategy?

In any way, this worked before 5.7.x with the default strategy and now it doesn't. Was it a bug that it worked before?

I've created a test-case here: https://github.com/SantoJambit/mikro-orm/blob/GH4899/tests/issues/GH4899.test.ts
It fails with default strategy and works with joined strategy.

[B4nan]

Interesting, let me take a closer look.

The end goal is to have both strategies work the same.

[SantoJambit]

Thanks!